Pericardial space - Erler Zimmer
In this specimen, the heart itself has been removed to illustrate the reflections of the parietal peritoneum and the orientation of the heart relative to other structures, including the diaphragm (diaphragmatic surface) and the lungs (left and right pulmonary surfaces). The pericardium is a multi-layered fibroserous sac that envelops the heart and remains continuous with the serous visceral pericardium (epicardium) covering the heart itself. In its usual anatomical position, the boundaries of the parietal pericardium coincide with the boundaries of the middle mediastinum (they are coterminous). The internal surface of the parietal peritoneum has been color-coded to facilitate the identification of the regions of the heart that typically reside in these segments of the middle mediastinum.
The base of the heart assumes a roughly rectangular shape and extends superiorly and posteriorly (anterior to the hilum of the lungs). This area is observable in the model as the most posterior surface that remains following the removal of the heart. It is primarily composed of the left atrium (pink) and, to a lesser extent, the right atrium (blue-green), along with the proximal segments of the great vessels (red and blue) as they enter and exit the heart. This region also serves as the "fixed" portion of the heart, securing the heart through the origins of the great vessels where the visceral and parietal serous pericardium are continuous. The transverse pericardial sinus (clinically relevant in certain cardiac surgical procedures) can be seen between the pulmonary arteries (red) and the bases of the superior vena cava, pulmonary trunk, and ascending aorta. Below the pulmonary veins, the depressed region formed by the left atrium and left ventricle is known as the oblique pericardial sinus.
Starting from the base, the heart projects anteriorly, inferiorly, and towards the left side of the thorax. The most inferior and lateral point is referred to as the apex. The apex is primarily formed by the inferolateral part of the left ventricle (yellow) and is typically located in the left fifth intercostal space along the midclavicular line.
Within the mediastinum, the heart rests on the diaphragmatic surface, which is primarily composed of the left ventricle and, to a lesser extent, the right ventricle (light green). This represents the lowest aspect of the heart and is separated from the base (the posterior surface) by the coronary sinus. It extends from the base of the heart to its apex, and on the model, it occupies the area that is just anterior and inferior to the ostium of the inferior vena cava.
The pulmonary surfaces constitute the wide and convex right and left lateral sides of the heart. The left pulmonary surface extends towards the left lung and is primarily composed of the left ventricle, while the right pulmonary surface extends towards the right lung and is composed mainly of the right atrium.
The heart also possesses an anterior surface that is predominantly made up of the right ventricle, with some right atrium on the right side and left ventricle on the left side. In this model, the anterior surface cannot be observed as it has been dissected beneath the anterior surface. The segment of the pericardium that is visible, being reflected to either side, would have originally covered a portion of the anterior surface before it was dissected.
Great Vessels
The aorta carries oxygenated blood from the heart into the systemic circulation. It begins as the ascending aorta and originates from the aortic orifice at the base of the left ventricle of the heart. The left and right coronary arteries branch off immediately superior to the aortic orifice from the left and right aortic sinuses, respectively, to supply the heart muscle itself. The vessel moves superiorly to the level of the second right costal cartilage, the sternal angle, and is then referred to as the arch of the aorta. It becomes the descending or thoracic aorta when the arch moves inferiorly to the vertebral level T4. It extends down to the T12 level and supplies a significant portion of the thorax.
The superior vena cava is a large vein primarily formed by the union of the right and left brachiocephalic veins. It drains directly into the right atrium at the SVC ostium, carrying a substantial portion of deoxygenated blood from the upper body.
The inferior vena cava is another large vein that drains a significant amount of deoxygenated blood from the lower body, with numerous tributaries contributing to it throughout the trunk. It also drains directly into the right atrium at the IVC ostium.
Pulmonary Vessels
The pulmonary trunk originates from the right ventricle of the heart. It bifurcates to give rise to the left and right pulmonary arteries, located to the left of the midline, just inferior to vertebral level T4/5 and the arch of the aorta. These arteries carry deoxygenated blood to the lungs, entering at the root of the lung in the hilum.
There are four pulmonary veins in total, with one superior and one inferior pulmonary vein for each side (left and right). They transport oxygenated blood from the lungs, beginning at the hilum and passing through the root of the lung, to the left atrium of the heart.
Transverse and Oblique Pericardial Sinus
The transverse sinus can be described as the common point where the parietal and visceral pericardium meet. It is located beneath the aorta and pulmonary trunk and has a tunnel-like appearance.
In contrast to the tunnel-like transverse sinus, the oblique pericardial sinus more closely resembles an ocean bay.
